2001 Lexus LX 470 Oil Pressure Guage

My Oil Pressure guage was erratically going from normal to low and even 0. I had it checked about 2 months ago by Lexus and they said it was Ok. It started acting up again, going from normal to low off and on. Now it is staying on 0. I had the oil changed, there are no noises or warning lights coming on, and the engine seems to run fine, even after going serveral hundred miles.

Do you think the oil pressure sending switch is bad? If so, where is it and is it something I can replace? I'm pretty handy, though not a mechanic.